Abstract:
According to the Encyclopedia Britannica a gel is a coherent mass consisting
of a liquid in which particles too small to be seen in an ordinary optical
microscope are either dispersed or arranged in a fine network throughout the
mass. A gel may be notably elastic and jellylike (as gelatin or fruit jelly),
or quite solid and rigid (as silica gel, a material that looks like coarse white
sand and is used as a dehumidifier) [32].
One can follow from this general definition that gels are low density open
network structures which can sustain a weak stress, and in this sense behave
like a solid. Like glasses, these are disordered arrested systems which do not
flow. A disordered material is characterized as a glass if its relaxation time
is very large. In a loose sense, gels are low density glasses but in fact, they
are different. Colloidal gels have dispersed particles in a solvent. Solvents
are often liquids but sometime they could be air, e.g., silica gel.
